Indomethacin shifts the peak of c-fos, egr-1, and c-myc gene expression in confluent fibroblasts induced by phorbol myristate acetate.

Phorbol 12-myristate 13-acetate (PMA) can induce transcription of a number of "early" genes in quiescent fibroblasts, although the biochemical steps intervening between activation of protein kinase c and changes in gene-regulatory proteins are only partially known. To investigate these pathways further, we have studied the effect of indomethacin (INDO) on the induction of expression by PMA of three early genes (c-fos, egr-1 and c-myc) in quiescent BALB/c 3T3 cells. INDO was found to markedly change the kinetics of PMA-induced c-fos and egr-1 gene expression, as measured by Northern analysis. As opposed to the normal peak of mRNA at 30 min and 30-60 min for c-fos and egr-1, respectively, the appearance of each peak in the presence of INDO was delayed by 30-60 min, although the amount of mRNA was approximately normal. By contrast, c-myc mRNA levels remained low for at least 3 hr. This effect on gene expression required concentrations of INDO (0.25-1 mM) which have previously been shown to inhibit cAMP-dependent protein kinases. The effect was reversible: after 75 min treatment with INDO followed by removal of the drug, c-fos was induced with normal kinetics by PMA. Cycloheximide superinduced the expression of c-fos, egr-1 and c-myc after PMA treatment; INDO inhibited this superinduction. Although its mode of action is not yet defined, the ability of INDO to perturb the kinetics of expression 3 PMA-inducible genes may make it a useful drug to study the signal transduction pathways involved in gene induction.